Comes from a spittlebug, family Cercopidae. The spit hides the nymphs from predators and protects against heat and cold. Easily removed with a stream of water, they do little if any harm. A very common sight in spring but they tend to disappear in summer.

Oh good. Thanks

It being a sucking pest I would think it might transmit plant viruses, as do aphids.

"As Cercopoidea are exclusively xylem feeders, and no viruses replicate in or are transported by plant xylem tissue, spittlebugs are potential vectors of only bacterial diseases."

Family-level Relationships of the Spittlebugs and Froghoppers (Hemiptera: Cicadomorpha: Cercopoidea), by Jason Cryan and Gavin Svenson

And never seen bacterial diseases to be an issue from these insects. Certainly not with the types of plants the spittle bugs prefer.

These nymphs turn into leaf-hopper bugs, the kind that shoot off like a bullet when touched.

As for them going to another part of your yard, the spittlebug will use any plant that has a somewhat dense, low-angle branching pattern to hold the spittle mass.

Most of the eggs have likely already been laid by the adults for this year; moving the lavender will not cause an immediate spittle-spread to nearby plants.

If you water-spray the spittle and it re-forms the next day, you did not spray hard enough. The nymphs are quite sticky.